Method of forming guanidine group on carbon nanotubes, method of attaching carbon nanotubes having guanidine groups to substrate, and carbon nanotubes and substrate manufactured by same

ABSTRACT

Disclosed herein is a method of forming a guanidine group on carbon nanotubes to improve the dispersibility of carbon nanotubes, a method of attaching carbon nanotubes having guanidine groups to a substrate, and carbon nanotubes and a substrate manufactured by the above methods. The method of forming the guanidine group on the carbon nanotubes includes forming a carboxyl group on the carbon nanotubes, and forming the guanidine group on the carboxyl group of the carbon nanotubes. In addition, the method of attaching the carbon nanotubes having guanidine groups to the substrate includes coating a substrate with a polymer having crown ether attached thereto, drying the polymer layer having crown ether attached thereto formed on the substrate to be semi-dried, and coating the semi-dried polymer layer with a solution including carbon nanotubes having guanidine groups dispersed therein. The carbon nanotubes having guanidine groups, which are manufactured by the method of the current invention, are hydrogen bonded with the solvent molecule capable of reacting with the guanidine group to form the hydrogen bond, and thus, are uniformly dispersed in the solvent. Further, by using the properties of the guanidine group capable of being selectively combined with crown ether, the carbon nanotubes having guanidine groups are aligned perpendicularly to the substrate at regular intervals thereon.

RELATED APPLICATION

The present application is based on, and claims priority from, KoreanApplication Number 2005-0007585, filed Jan. 27, 2005, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, generally, to methods of forming aguanidine group on carbon nanotubes (CNTs) and of attaching CNTs havingguanidine groups to a substrate, and CNTs and a substrate manufacturedby the above methods. More specifically, the present invention relatesto a method of forming a guanidine group on CNTs to improve thedispersibility of CNTs, a method of attaching CNTs having guanidinegroups to a substrate by combining the guanidine group with the crownether, and CNTs and a substrate manufactured by the above methods.

2. Description of the Related Art

Dispersion of CNTs is essential for all pre-treatment processes usingthe CNTs. However, in cases where the CNTs are dispersed in water or aprotic solvent, it is difficult to uniformly disperse the CNTs, composedcompletely of carbons, in the solvent. Therefore, a dispersing agent,such as a surfactant, is used. To achieve the uniform dispersion of theCNTs, the CNTs that are partially negatively charged should be formed inthe shapes of micelles or inverse micelles including CNTs surrounded bythe dispersing agent. As such, the dispersing agent is used in apredetermined concentration or more. In addition, various dispersingagents, such as nonionic-, cationic-, anionic-, and polymeric-typedispersing agents, are typically used. However, the dispersing agentsurrounding the CNTs may function as an impurity in the process of usingthe CNTs.

Hence, since the dispersing agent used for the dispersion of the CNTsmay cause problems in the subsequent process, methods of introducing afunctional group able to directly react with the solvent to the CNTshave been proposed to uniformly disperse the CNTs while solving theabove problems. For example, methods of forming a carboxyl group, ahydroxy group or an amine group on CNTs have been known.

In this regard, U.S. Pat. No. 6,368,569 discloses a method of forming acarboxyl group on CNTs, and U.S. Pat. Nos. 6,187,823 and 6,331,262disclose a method of forming an amine group on CNTs. When the carboxylgroup (—COOH) as a hydrophilic functional group is introduced to theCNTs, the CNTs are surrounded with water molecules due to the hydrogenbond between the carboxyl group and the water molecule of H—O—H. Thus,the CNTs are uniformly dispersed at regular intervals in water, evenwithout the use of the dispersing agent. The amine group, which is ahydrophilic functional group, is hydrogen bonded with a water moleculeso that the CNTs are dispersed in the solvent.

However, in the cases where a metal cation is present in the solution,the carboxyl group or amine group of the CNTs may be undesirablychelated with the metal cation.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the related art, and an object of thepresent invention is to provide a method of forming a guanidine group,which is not chelated with a metal cation present in a solution, onCNTs.

Another object of the present invention is to provide a method offorming a guanidine group on CNTs to increase the dispersibility ofCNTs.

A further object of the present invention is to provide a method ofattaching CNTs having guanidine groups to a substrate.

Yet another object of the present invention is to provide CNTs havingguanidine groups.

Still another object of the present invention is to provide a substratehaving CNTs attached thereto.

In order to accomplish the above objects, according to a first aspect ofthe present invention, a method of forming a guanidine group on CNTs isprovided, which comprises forming a carboxyl group on CNTs; and forminga guanidine group on the carboxyl group of the CNTs.

According to a second aspect of the present invention, CNTs areprovided, which comprise one or more bonded moieties, in which themoiety is represented by Formula 1, below:

According to a third aspect of the present invention, a method ofattaching CNTs having guanidine groups to a substrate is provided, whichcomprises coating a substrate with a polymer having crown ether attachedthereto; drying the polymer layer having crown ether attached theretoformed on the substrate to be semi-dried; and coating the semi-driedpolymer layer with a solution including CNTs having guanidine groupsdispersed therein.

According to a fourth aspect of the present invention, a method ofattaching CNTs having guanidine groups to a substrate is provided, whichcomprises reacting a polymer having crown ether attached thereto withCNTs having guanidine groups, to prepare a polymer having a combinationof crown ether and CNTs having guanidine groups; and coating a substratewith the polymer having a combination of crown ether and CNTs havingguanidine groups.

According to a fifth aspect of the present invention, a method ofattaching CNTs having guanidine groups to a substrate is provided, whichcomprises manufacturing a polymer having crown ether attached theretointo a semi-dried film; and coating the semi-dried film with a solutionincluding CNTs having guanidine groups dispersed therein.

According to a sixth aspect of the present invention, a method ofattaching CNTs having guanidine groups to a substrate is provided, whichcomprises reacting a polymer having crown ether attached thereto withCNTs having guanidine groups, to prepare a polymer having a combinationof crown ether and CNTs having guanidine groups; and manufacturing thepolymer having a combination of crown ether and CNTs having guanidinegroups into a semi-dried film.

According to a seventh aspect of the present invention, a method ofattaching CNTs having guanidine groups to a substrate is provided, whichcomprises dipping an anodized aluminum oxide (AAO) substrate that isinstalled to a cathode into a solution including CNTs having guanidinegroups dispersed therein; and performing electrophoresis orelectroplating.

According to an eighth aspect of the present invention, a substratehaving CNTs attached thereto is provided, which comprises a substrate; apolymer layer having crown ether attached thereto; and a coating layerof CNTs having one or more bonded moieties, in which the moiety isrepresented by Formula 1, below:

According to a ninth aspect of the present invention, a substrate havingCNTs attached thereto is provided, which comprises a substrate; and apolymer layer formed by reacting a polymer having crown ether attachedthereto with CNTs having one or more bonded moieties, in which themoiety is represented by Formula 1, below:

According to a tenth aspect of the present invention, a substrate havingCNTs attached thereto is provided, which comprises an AAO substrate; andCNTs having one or more bonded moieties inserted into pores of thesubstrate, in which the moiety is represented by Formula 1, below:

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 a is a molecular model photograph showing the molecularrecognition between 18-crown-6-ether and guanidine;

FIG. 1 b is a view showing a three-dimensional molecular model of FIG. 1a;

FIG. 2 is an FT-IR spectrum of CNTs having the carboxyl group preparedin Example 1, according to the present invention;

FIG. 3 is a graph showing the dispersibility of CNTs having nofunctional group using Near IR spectroscopy;

FIG. 4 is a graph showing the dispersibility of CNTs having guanidinegroups, according to the present invention; and

FIG. 5 is a view showing a substrate having multi-walled CNTs alignedperpendicularly to the substrate at regular intervals thereon, accordingto the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a detailed description will be given of the presentinvention.

The present invention pertains to a method of forming a guanidine groupon CNTs so that the CNTs are uniformly dispersed in a solvent. The CNTshaving guanidine groups, manufactured by the method of the presentinvention, are uniformly dispersed in the solvent that is able to reactwith the guanidine group to form a hydrogen bond, even without anadditional dispersant. In addition, in the case where a metal cation ispresent in the solvent, the CNTs having guanidine groups of the presentinvention are not chelated with the metal cation.

The CNTs are classified in accordance with the manufacturing methodthereof and the number of walls thereof. In the case where the CNTs areclassified depending on the number of walls, single-walled carbonnanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) aretypically used. Further, in the classification based on themanufacturing method, there are CNTs resulting from CVD (Chemical VaporDeposition) and CNTs obtained by arc-discharge. In addition, two typesof CNTs, that is, SWNTs and MWNTs may be formed according to eachmanufacturing method. In the present invention, all of the CNTsmentioned above may be used.

With the aim of preparing a functional site required to form theguanidine group on the CNTs, a carboxyl group is formed on the CNTs. Forthis, the CNTs are added to a mixture of nitric acid and sulfuric acidmixed at a volume ratio of 3:1 so that the ratio of the volume ofmixture to the weight of CNTs is 8000:1, heated to a predeterminedtemperature, and reacted with sonication, thereby forming a —COOH groupon the CNTs. While the —COOH group is formed, an —OH group isadditionally formed. As such, the amount of CNTs may be increased ordecreased in the range of ±20%. Since the CNTs are composed of stablebonds between the carbons, they require high activation energy fordissociation of stable C—C bonds and the introduction of anotherfunction group. Thus, the CNTs are heated to about 50-60° C., and thenreacted for about 22-26 hr, and preferably, for 24 hr, with sonication.If the temperature is lower than 50° C., the activation energy does notreach the level required for reaction, and thus the reaction does nottake place. Meanwhile, if the temperature is higher than 60° C.,economic benefits are negated. In addition, the reaction time shorterthan 22 hr results in insufficient C—C bond dissociation in the CNTs.Also, the dissociated C—C bonds are not oxidized, and thus, areundesirable. Conversely, even if the reaction time exceeds 26 hr, thedissociation of C—C bonds is not further promoted.

The vibration energy of C—C bonds increases due to heating andsonification, whereby the dissociation of C—C bonds is promoted. Inparticular, the C—C bonds are dissociated at terminal or defectiveportions of the CNTs. Further, since delocalized π-electrons are presenton the surface of CNTs, the C—C bonds may be easily dissociated. Thecarbons, which are present on the terminal portions of the CNTs, haveonly two or three bonds and thus are unstable. Therefore, highlyreactive C—C bonds are easily dissociated, whereby the CNTs are cut intopredetermined sizes due to such dissociation of C—C bonds.

While the C—C bonds are dissociated, bond electrons are localized to anyone atom, thereby forming carbon ions, such as C⁺ and C⁻, or theelectrons are equally distributed to the two carbons, forming radicalions. In addition, since the used nitric acid and sulfuric acid arehighly reactive and the dissociated carbon ions or carbon radicals arealso unstable, and therefore highly reactive, the reaction therebetweenmay easily occur. Therefore, the —COOH group is formed on thedissociated C—C bond portion of the CNTs through the oxidation. In sucha case, the —OH group may be further formed thereon. The oxidation takesplace due to the nitric acid and sulfuric acid used.

In the CNTs having —COOH group (hereinafter, referred to as‘CNTs-COOH’), the guanidine group is bonded to the —COOH group throughthe amide or peptide formation reaction between the —COOH group and theguanidine group in the compound having the guanidine group. Theguanidine group is formed on CNTs-COOH as represented by Reaction 1,below:

As is apparent from Reaction 1, the CNTs having one or more bondedmoieties are formed, in which the moiety is represented by Formula 1.Although the number of moieties of Formula 1 is not particularlylimited, it is determined so that the equivalence ratio of the CNTs tothe moiety of Formula 1 is in the range of from 1:1 to 1:2. As such,when the excess equivalent number of guanidine groups is added or theexcess coupling agent is added, the CNTs and the moiety of Formula 1 maybe bonded at the equivalence ratio of 1:2.

CNTs-COOH react with the compound having the guanidine group(hereinafter, referred to as ‘guanidine reactant’) in an inertatmosphere, for example, but without being limited to, a nitrogen orargon atmosphere. In this case, the coupling agent is added for theamine formation reaction between —COOH and guanidine. The guanidinereactant includes, but is not limited to, guanidine represented byFormula 2, below, cyanoguanidine represented by Formula 3, below, orguanidine thiocyanide represented by Formula 4, below.

Since the guanidine reactant reacts with CNTs-COOH at the equivalenceratio of 2:1, the guanidine reactant is reacted with CNTs-COOH inconsideration of the above condition. For example, if the guanidinereactant is used in a larger amount than CNTs-COOH, exceeding the aboveequivalence ratio, and if the coupling agent remains, the non-reactiveguanidine reactant may react with the remaining coupling agent, henceforming the by-products.

In addition, the coupling agent includes, for example,1-(3-dimethylaminopropyl)-3-ethyl-carboimide hydrochloride (EDC),dicyclohexylcarbodiimide (DCC), oxalic acid, or oxalic acid chloride.

The formation of guanidine group is achieved by reacting CNTs-COOH, theguanidine reactant and the coupling agent in the presence of the solventfor 6-10 hr while stirring them at 25-50° C. If the reaction temperatureis lower than 25° C., the activation energy required for the reaction isnot obtained. On the other hand, if the reaction temperature exceeds 50°C., the activation energy required for the reaction is increased andthus the reaction occurs quickly. However, the molecules may beundesirably dissociated. In addition, when the reaction time is lessthan 6 hr, the activation energy required for the reaction of moleculesis not undesirably provided. Conversely, if the reaction time exceeds 10hr, over-reaction may occur between the molecules. Also, the by-productsand the reaction product having low stability may be formed.

Since the coupling agent used for the reaction acts as the kind ofcatalyst, it is used in a catalytic amount. For example, the couplingagent is used in an amount of 0.4-0.5 equivalents, based on 1 equivalentof CNTs-COOH. If the coupling agent is used in an amount less than 0.4equivalents, the activation of carbonyl group is low, obtaining CNTshaving guanidine groups at low yields. On the other hand, the use ofcoupling agent exceeding 0.5 equivalents negates economic benefits. Thesolvent used for the formation of guanidine group includesdichloromethane.

When the carboxyl group and the guanidine group are introduced to theCNTs, processes accompanied to CNTs washing, neutralization, filtration,separation, removal of impurities, etc., may be performed according totechniques known in the art, if required.

The guanidine group consists of two NH₂ single bonded to central carbonand one NH double bonded thereto, and is a strongly basic functionalgroup having high pKa or pH. In addition, the guanidine group has threenitrogen atoms having high charge density (or lone pair electrons) onwhich charges are distributable. Hence, the CNTs having guanidine groupsare further effectively dispersed in the solvent, attributed to the moreuniform charge distribution, compared to conventional CNTs havingcarboxyl groups or amine groups. Moreover, in the case which theguanidine group is electrically charged by changes in the pH of thesolution, charges are uniformly distributed on the three nitrogen atomsof the guanidine group, causing electrostatic interactions in the CNTshaving guanidine groups. Thereby, the CNTs having guanidine groups areuniformly dispersed in an aqueous solution. The charge distribution ofthe guanidine group in the acidic solution is represented by Formula 5,below:

Therefore, the CNTs having guanidine groups (hereinafter, referred to as‘CNTs-CO—(NH)₂NH₂’) are present in the state of being uniformlydispersed. The reason is that CNTs-CO—(NH)₂NH₂ are disposed atpredetermined intervals required for the interactions between the CNTsand the solvent molecule and between the two CNTs, due to the hydrogenbond formed by the interaction between the guanidine group and thesolvent, or due to the repulsive force caused by the electrostaticinteraction of CNTs-CO—(NH)₂NH₂ through the charge distribution.

That is, CNTs-CO—(NH)₂NH₂ are uniformly dispersed at regular intervalsin any solvent able to react with a guanidine group to form a hydrogenbond, for example, water (e.g., deionized water or 3^(rd) distilledwater), or a protic solvent, such as alcohol including methanol,ethanol, isopropylalcohol, etc.

Whether the guanidine group has been formed on the CNTs is confirmedusing FT-IR, Raman or XPS analysis.

On the other hand, since the guanidine group is selectively combinedwith the crown ether molecule, CNTs-CO—(NH)₂NH₂ may be attached to thesubstrate so as to be aligned perpendicularly to the substrate atregular intervals thereon.

Thus, the present invention provides a substrate including CNTs havingone or more bonded moieties attached thereto, in which the moiety isrepresented by Formula 1.

Below, a method of attaching CNTs-CO—(NH)₂NH₂ to the substrate isparticularly described.

Since the structure of the cyclic crown ether moleculethree-dimensionally corresponds to that of the tripod-shaped guanidinegroup as in the relationship between key and lock, the guanidine groupis selectively combined with the crown ether. In addition, the guanidinegroup and the crown ether molecule may be selectively combined, eventhough undergoing influences due to the electrostatic interactions.

That is, the electrostatic interactions between non-shared electronpairs of oxygen on the ether molecule and hydrogen on the guanidinemolecule are caused by the molecular recognition of the crown ether andthe guanidine group. Thus, the crown ether and the guanidine arespontaneously combined even without an external driving force, due tothe size effect and hydrogen bond through the above electrostaticinteractions. The integrally combined crown ether and guanidine group isshown in FIGS. 1 a and 1 b.

In the attachment of CNTs-CO—(NH)₂NH₂ at regular intervals to thesubstrate, the substrate includes, for example, copper, aluminum ornickel metal substrate, or a polymer film having crown ether attachedthereto or a polymer film having a combination of crown ether andguanidine. For the reaction between the crown ether and the guanidinegroup of CNTs-CO—(NH)₂NH₂ when attaching the CNTs-CO—(NH)₂NH₂ to themetal substrate, the substrate is coated with the polymer having crownether attached thereto, before CNTs-CO—(NH)₂NH₂ are attached to thesubstrate. Likewise, the polymer having crown ether attached thereto isreacted with CNTs-CO—(NH)₂NH₂ to form the polymer having a combinationof crown ether and guanidine, which is then applied on the substrate,thereby manufacturing a substrate on which the CNTs are alignedperpendicularly to the substrate. The polymer film having crown etherattached thereto to which the CNTs are attached, or the polymer filmhaving a combination of crown ether and guanidine of CNTs-CO—(NH)₂NH₂may be used in electronic devices requiring flexibility, for example,displays.

The polymer having crown ether attached thereto is obtained bydispersing crown ether and a polymer in a solvent and then reacting themwhile stirring at room temperature (about 20-25° C.) for about 2-5 hr.If the reaction time is less than 2 hr, the resultant reaction productmay undesirably have a molecular weight corresponding to oligomers oranalogues thereof, rather than the molecular weight of a polymer.Meanwhile, the reaction time exceeding 5 hr results in negated economicbenefits.

The crown ether includes, for example, but is not limited to, 18-membercrown ether represented by Formula 6, below, dibenzo-18-crown-6-etherrepresented by Formula 7, below, and dibenzo-24-member crown etherrepresented by Formula 8, below:

The molecular sizes of the crown ethers represented by Formulas 6 to 8are suitable for bonding with the guanidine groups represented byFormulas 2 to 4.

The polymer includes a conductive polymer selected from amongpolyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), and poly(4-vinylphenols), orpolymethylmethacrylates (PMMA), polystyrenes (PS), or derivativesthereof. The derivative of the polymer means a material bonded with adopant to increase the electron mobility of the polymer, which isgenerally known in the art. The mixture ofpoly(3,4-ethylenedioxythiophene) and poly(styrenesulfonic acid)(PEDOT:PSS) is called Baytron P, which is available from Bayer AG,Germany, and includes poly(3, 4-ethylenedioxythiophene) andpoly(styrenesulfonic acid) mixed at a ratio of about 4:6.

As for the metal substrate having high conductivity, the general polymeras mentioned above is usable. When the metal substrate having lowconductivity is coated with the polymer having crown ether attachedthereto or the polymer having a combination of crown ether andguanidine, although the general polymer as mentioned above is used, theuse of the conductive polymer is more preferable. In the case where thepolymer film having crown ether attached thereto or the polymer filmhaving a combination of crown ether and guanidine of CNTs-CO—(NH)₂NH₂ isused as the substrate, the conductive polymer is used. This is becauseCNTs-attached assemblies, which are used as field emission devices orelectronic devices such as displays, require high conductivity.

The conductivity of the metal substrate may vary with the dopant to beadded when manufacturing the metal substrate, which is generally knownto those skilled in the art. Those skilled in the art may appropriatelyuse the conductive polymer, depending on the conductivity of the metalsubstrate and the conductivity required for electronic devices.

The polymer having crown ether attached thereto is prepared using asolvent, such as pyridine or pyrrolidine.

In the reaction of polymer and crown ether, the crown ether is used inan amount of 10-20 parts by weight, based on 100 parts by weight of thepolymer. When the amount of crown ether is less then 10 parts by weight,the crown ether attaches less to a side chain of the polymer, and thus,may not be uniformly formed at desired intervals on the coating surface.On the other hand, if the amount of crown ether exceeds 20 parts byweight, a large amount of crown ether is undesirably attached to theside chain of the polymer, or the likelihood of the crown ether becomingattached to other positions, as well as the side chain of the polymer,undesirably increases.

The polymer having crown ether attached thereto is applied on the metalsubstrate, or is reacted with CNTs-CO—(NH)₂NH₂ to be formed into apolymer having a combination of crown ether and guanidine or a film. Thecoating process and the film preparation process may be performed by anymethod known in the art, and are not particularly limited. The coatingprocess may be performed by, but is not limited to, any method known inthe art, for example, spin coating, dip coating, spray coating, flowcoating, or screen printing. The film is mainly obtained using aprinting process.

The coating layer is formed to a thickness of about 200-1000 μm on onesurface of the metal substrate. In addition, the film is prepared to beabout 1-2 mm thick. As such, the thickness of the coating layer or filmis not particularly limited for the attachment of the CNTs. However, inthe coating layer or film to which the CNTs have been attached for usein field emission devices or other electronic devices, since theconductivity or resistance varies with the thickness of the above layeror film, the coating layer or film is preferably formed in the abovethickness range.

The coating layer or film of the polymer having crown ether attachedthereto is dried in a semi-dry state of B-step. Herein, the semi-drystate means that a predetermined target is partially dried. For this, adrying process is performed at about 50-80° C. for about 3-10 hr.

Subsequently, the semi-dried coating layer or film is coated with thesolution including CNTs-CO—(NH)₂NH₂ dispersed therein. The solutionincluding CNTs-CO—(NH)₂NH₂ dispersed therein is prepared by dispersingCNTs-CO—(NH)₂NH₂ in the water or the protic solvent, such as alcohol. Assuch, since the guanidine group formed on the CNTs in the solutionreacts with the crown ether in the coating layer, the amount ofCNTs-CO—(NH)₂NH₂ to be dispersed in the solvent corresponds to1/100-1/500, based on the weight of the polymer having crown etherattached thereto. The reason why the amount is limited as mentionedabove is described below.

The semi-dried coating layer or film of the polymer having crown etherattached thereto is coated with the solution having CNTs-CO—(NH)₂NH₂dispersed therein, thus combining the crown ether with the guanidinegroup. Thereby, the CNTs are attached to the substrate while beingaligned perpendicularly to the substrate at regular intervals thereon.

The reaction between guanidine and crown ether takes place according tothe self-assembly manner (Molecular recognition method), without theneed for additional external conditions. Thus, the coating layer or filmof the polymer having crown ether attached thereto is coated with thesolution including CNTs-CO—(NH)₂NH₂ dispersed therein, resulting inspontaneously combined crown ether and guanidine. That is, crown etherand guanidine are spontaneously reacted at room temperature (e.g.,20-25° C.) and at neutral pH, to form a combination therebetween.

The substrate having CNTs aligned perpendicularly to the substrate atregular intervals thereon is manufactured by reacting CNTs-CO—(NH)₂NH₂with the polymer having crown ether attached thereto, to prepare apolymer having a combination of guanidine and crown ether, which is thenapplied on the substrate, or which is then formed into a film.

That is, the polymer having crown ether attached thereto is added alongwith CNTs-CO—(NH)₂NH₂ to the solvent and then reacted while beingstirred at room temperature for 20-40 min. Thereby, the guanidine groupof the CNTs is combined with the crown ether, and thus, the polymerhaving a combination of guanidine and crown ether is formed. As such,the reaction solvent includes, for example, pyridine, pyrrolidine,methylene chloride, etc. In addition, CNTs-CO—(NH)₂NH₂ are added in anamount of 1/100-1/500, based on the weight of the polymer having crownether attached thereto, to the solvent. Since the CNTs are nano-sized,great numbers of CNTs are provided, despite the very small weight.Hence, the above amount of CNTs-CO—(NH)₂NH₂ is sufficient to react withcrown ether bonded to the polymer. As for the control of emission sitedensity for application to field emission devices, CNTs-CO—(NH)₂NH₂ arepreferably used in the above amount range because too many CNTs per unitarea may negatively affect the emission of electrons. WhenCNTs-CO—(NH)₂NH₂ are used in an amount less than a lower limit, thenumber of CNTs to be aligned is low, and thus, the CNTs may not exhibitmaximal effects in field emission devices or electronic devices.Meanwhile, if the amount of CNTs-CO—(NH)₂NH₂ exceeds an upper limit,non-reactive CNTs excessively remain due to the limited number of crownether molecules present on the surface, thus negating economic benefits.

Then, the polymer having a combination of crown ether and guanidine ofCNTs-CO—(NH)₂NH₂ is applied on the substrate, and then dried, therebymanufacturing a substrate having CNTs aligned perpendicularly to thesubstrate at regular intervals thereon. The coating process may beperformed as in the above manner.

In addition, the polymer having a combination of crown ether andguanidine of CNTs-CO—(NH)₂NH₂ is shaped into a film, therebymanufacturing a substrate having CNTs aligned perpendicularly to thesubstrate at regular intervals thereon.

Further, CNTs-CO—(NH)₂NH₂ are inserted into small pores in the AAOsubstrate through electrophoresis or electroplating, and thus,CNTs-CO—(NH)₂NH₂ are attached to the AAO substrate to be uniformlyaligned thereon. The AAO substrate may consist of any anodized aluminumoxide prepared by any method.

The positively charged CNTs are inserted into 500-700 nm deep pores inthe AAO template installed to a cathode through electrophoresis orelectroplating. At this time, this process is performed at a DC currentof 20-50 V for 10-20 min. The electrophoresis or electroplating usingthe AAO template is preferably carried out in the acidic solution, pH3-5. This is because CNTs-CO—(NH)₂NH₂ have a high charge characteristicin the acidic solution, whereby it is easily movable toward the AAOtemplate.

In the insertion of the CNTs into the AAO pores through theelectrophoresis or electroplating, if the CNTs have no polar functionalgroup, the mobility and strength of the CNTs are lowered even whenapplying the current for electrophoresis or electroplating.

However, the guanidine group as a polar functional group inCNTs-CO—(NH)₂NH₂ of the present invention is more easily moved to theAAO substrate when the current is applied to the CNTs. As well,CNTs-CO—(NH)₂NH₂ manufactured by the method of the present inventionhave a smaller size and higher charge characteristic than conventionalCNTs surrounded with dispersing agent. Therefore, when CNTs-CO—(NH)₂NH₂are attached to the AAO substrate through electrophoresis orelectroplating, the CNTs are perpendicularly inserted into small poresof the AAO template.

In addition, since CNTs-CO—(NH)₂NH₂ show opposite type charge in respectto changes in pH, the CNTs may be attached while changing the value ofpH, depending on the kinds of substrate to which the CNTs are to beattached.

A better understanding of the present invention may be obtained in lightof the following examples which are set forth to illustrate, but are notto be construed to limit the present invention.

EXAMPLE 1

40 mg of MWNTs (Iljin Nanotech Co. Ltd., Korea) were added to a mixtureof 60 ml of H₂SO₄ and 20 ml of HNO₃, and then reacted for 24 hr withultra-sonication at 50° C. As such, the sonication was performed atabout 30 kHz. The strongly acidic reaction solution was diluted withdeionized water to be a neutral solution, and filtered using a vacuumfilter.

The filtration process was carried out using a filter paper having apore size of 0.5-1 μm. The filtrate was diluted and washed several timeswith deionized water until pH reached a neutral value. At this time, pHwas measured using a litmus paper. The neutralized MWNTs-COOH solutionwas dried at 80° C. for 6 hr. Then, whether the COOH group had beenformed on the dried MWNTs-COOH was confirmed using FT-IR. The resultsare shown in FIG. 2. As shown in FIG. 2, a peak corresponding to C═O isshown at 1700 cm⁻¹ and a peak corresponding to O—H at 3300 cm⁻¹. Fromthis, it can be found that —COOH group is formed on the CNTs.

EXAMPLE 2

10 mg of MWNTs-COOH prepared in Example 1, 20 mg of guanidine, and 5 mlof 2 M oxalic acid were dissolved in dichloromethane in an argon inertatmosphere, and then reacted at 50° C. for about 6 hr in an argon inertatmosphere, to introduce a guanidine group to a —COOH group formed onthe MWNTs. The reaction solution was filtered to remove by-productstherefrom, yielding a reaction product, MWNTs-CO—(NH)₂NH₂ represented byFormula 9, below. The filtration process was performed using a filterpaper having a pore size of 0.5-1 μm.

EXAMPLE 3

The dispersibility of MWNTs-CO—(NH)₂NH₂ prepared in Example 2 wasmeasured.

As such, the dispersibility was assayed by measuring dispersionstability and dispersion state of MWNTs having no functional group andMWNTs-CO—(NH)₂NH₂ using Turbiscan.

The dispersion stability is determined to the extent that the particlesare stably maintained at regular intervals from each other in thesolvent or from the solvent molecule for a long period of time. Thedispersion stability was assayed by changes in the average value oftransmittance varying with the time.

The dispersion state is determined to the extent that the particles areuniformly dispersed in the vessel at a predetermined point in time, andis an index showing no settlement or agglomeration of particles. Thedispersion state was assayed by the difference between the maximal valueand the minimal value of the transmittance measured at the same time.

5 mg of MWNTs having no functional group were dispersed in 100 ml ofdeionized water, with sonication at 30 kHz, to obtain a dispersedsolution, which was exposed to near infrared rays for 12 hr. As such,transmittance was measured every 1 hr for a total of 12 hr usingTurbiscan. The results are shown in FIG. 3, in which the dispersionstability and dispersion state of MWNTs having no functional groupdispersed in the aqueous solution are shown. In the graph shown in FIG.3, the dispersion stability shows the change in transmittance of 28.82%for 12 hr, and the dispersion state shows the change in transmittance of12.66%. Further, it appears that MWNTs are settled, or MWNTs agglomerateamong themselves, forming large particles, over time.

Meanwhile, 5 mg of MWNTs-CO—(NH)₂NH₂ were dispersed in 100 ml ofdeionized water, with sonication at 30 kHz, to obtain a dispersedsolution, which was exposed to near infrared rays for 12 hr. As such,transmittance was measured every 1 hr for a total of 12 hr usingTurbiscan. The results are shown in FIG. 4. In the graph shown in FIG.4, although the transmittance is little changed and its difference isnot distinguished in the drawing, the dispersion stability shows thechange in transmittance of 4.974% for 12 hr, and the dispersion stateshows the change in transmittance of 1.205%. That is, compared to MWNTshaving no functional group in which the difference of the average valueof transmittance for 12 hr is 28.82% and the difference between themaximal value and the minimal value of transmittance measured at thesame time is 12.66%, the aqueous solution including MWNTs-CO—(NH)₂NH₂dispersed therein has the smaller values. From this, it can be foundthat the dispersion stability and dispersion state of MWNTs-CO—(NH)₂NH₂are further increased to 5.70 times and 10.5 times, respectively, thusexhibiting better dispersibility.

EXAMPLE 4

5 g of a polystyrene polymer and 1 g of dibenzo-18-crown-6-ether weredissolved in 500 ml of pyridine and then reacted for about 5 hr whilebeing stirred at room temperature using a magnetic stirrer at 200 rpm.500 ml of deionized water was added to the reaction solution. By addingthe deionized water, polystyrene having crown ether attached thereto wasdispersed in deionized water, while by-products, such as non-reactivematerials, were dispersed in the pyridine solvent, in which deionizedwater and pyridine were separated due to the difference in densitytherebetween. Thus, the deionized water was separated from the pyridinesolvent using a separate funnel, whereby the polystyrene having crownether attached thereto was removed from the non-reactive by-products.The pyridine solvent was distilled off, yielding a polystyrene polymerhaving crown ether attached thereto, represented by Formula 10, below:

The product of Formula 10 thus obtained was spin applied to a filmthickness of 200 μm on one surface of a 1 mm thick copper substrate, andthen dried in a semi-dry state of B-step at 50° C.

Subsequently, 10 mg of MWNTs-CO—(NH)₂NH₂ prepared in Example 2 weredispersed in 100 ml of ethanol, and then spin applied to a thickness of200 μm on the semi-dried coating layer. Thereby, due to the reactionbetween the crown ether in the coating layer and the guanidine group,MWNTs was aligned perpendicularly to the substrate at regular intervalson the substrate. The substrate having MWNTs aligned perpendicularly tothe substrate at regular intervals thereon is shown in FIG. 5.

EXAMPLE 5

5 g of the polystyrene polymer having crown ether attached thereto ofFormula 10, prepared in Example 4, was added to 500 ml of pyridine anddispersed therein while being stirred at 200 rpm using a magneticstirrer. Then, 10 mg of MWNTs-CO—(NH)₂NH₂ prepared in Example 2 wereadded to the above dispersed solution and reacted for about 30 min whileweakly stirring them at 100 rpm using a magnetic stirrer. After thecompletion of the reaction, the guanidine group attached to MWNTs wasintroduced to the crown ether, as shown in FIG. 1 b, thus obtaining apolystyrene polymer having a combination of guanidine group and crownether.

The deionized water was added to the above reaction product, and hence,the polystyrene polymer having a combination of guanidine group andcrown ether was dispersed in deionized water, while the by-products,such as non-reactive materials, were dispersed in the pyridine solvent,in which the deionized water and pyridine were separated due to thedifference in density therebetween. Thus, the deionized water wasseparated from the pyridine solvent using a separate funnel, whereby thepolystyrene polymer having a combination of guanidine group and crownether was removed from the non-reactive by-products. The pyridinesolvent was distilled off, yielding a polystyrene polymer having acombination of guanidine group and crown ether formed by introducing theguanidine group of MWNTs-CO—(NH)₂NH₂ to the crown ether.

The polymer having a combination of guanidine and crown ether thusobtained was spin applied to a thickness of 200 μm on one surface of a 1mm thick nickel substrate, and then dried at 70° C., thus obtaining asubstrate having MWNTs aligned perpendicularly to the substrate atregular intervals thereon.

EXAMPLE 6

The polystyrene polymer having crown ether attached thereto of Formula10, prepared in Example 4, was manufactured into a 1.5 mm thick film,which was then dried in a semi-dry state of B-step at 50° C. Thereafter,10 mg of MWNTs-CO—(NH)₂NH₂ prepared in Example 2 were dispersed in 100ml of ethanol, to obtain a dispersed solution, which was then spinapplied to a thickness of 200 μm on the above semi-dried polymer film.After the coating process, the crown ether in the coating layer reactedwith the guanidine group, resulting in a polymer film having MWNTsaligned perpendicularly to the polymer film at regular intervalsthereon.

EXAMPLE 7

The polystyrene polymer having a combination of guanidine group andcrown ether, prepared in Example 5, was manufactured into a 1.5 mm thickfilm, and then dried at 70° C., thereby obtaining a polymer film havingMWNTs aligned perpendicularly to the film at regular intervals thereon.

EXAMPLE 8

An AAO template having pores about 600 nm in diameter and a Pt electrodewere installed as a cathode and an anode, respectively. Further, asolution of 10 mg of MWNTs-CO—(NH)₂NH₂ of Example 2 dissolved in 200 mlof deionized water was used, and a DC current of 40 V was applied, toperform electrophoresis. The electrophoresis was conducted for about 15min. Thereby, MWNTs-CO—(NH)₂NH₂ were moved and inserted into the poresof the AAO template, thus obtaining a substrate having MWNTs-CO—(NH)₂NH₂vertically inserted into its pores.

As mentioned above, the present invention provides methods of forming aguanidine group on CNTs and of attaching CNTs having guanidine groups ona substrate, and CNTs and a substrate manufactured by the above methods.The CNTs having guanidine groups of the present invention are hydrogenbonded with the solvent that is able to react with the guanidine groupto form the hydrogen bond, and thus, are uniformly dispersed in thesolvent. Further, since the guanidine group has three nitrogen atoms onwhich charges are distributable, the CNTs having guanidine groups areuniformly dispersed in the solvent through the electrostaticinteractions due to the uniform charge distribution. By using theproperties of the guanidine group able to be selectively combined withthe crown ether, the CNTs having guanidine groups are alignedperpendicularly to the substrate at regular intervals on the substrate.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A method of forming a guanidine group on carbon nanotubes,comprising: forming a carboxyl group on carbon nanotubes; and forming aguanidine group on the carboxyl group of the carbon nanotubes.
 2. Themethod as set forth in claim 1, wherein the forming of the carboxylgroup is performed by adding the carbon nanotubes to a mixture of nitricacid and sulfuric acid mixed at a volume ratio of 3:1, and then reactingthe carbon nanotubes and the mixture of nitric acid and sulfuric acidfor 22-26 hr with sonification at 50-60° C.
 3. The method as set forthin claim 1, wherein the forming of the guanidine group is performed byadding the carbon nanotubes having the carboxyl group, a compound havinga guanidine group, and a coupling agent to a solvent, and then reactingthe carbon nanotubes, the compound having the guanidine group, and thecoupling agent, at 25-50° C. for 6-10 hr in an inert atmosphere.
 4. Themethod as set forth in claim 3, wherein the compound having theguanidine group is selected from among guanidine, cyanoguanidine, andguanidine thiocyanide.
 5. The method as set forth in claim 3, whereinthe coupling agent is selected from among1-(3-dimethylaminopropyl)-3-ethyl-carboimide hydrochloride (EDC),dicyclohexylcarbodiimide (DCC), oxalic acid, and oxalic acid chloride.6. The method as set forth in claim 3, wherein the coupling agent isused in an amount of 0.4-0.5 equivalents, based on 1 equivalent of thecarbon nanotubes having the carboxyl group.
 7. A carbon nanotube,comprising one or more bonded moieties, wherein the moiety isrepresented by Formula 1, below:


8. A method of attaching carbon nanotubes having guanidine groups to asubstrate, comprising: coating a substrate with a polymer having crownether attached thereto; drying the polymer layer having crown etherattached thereto formed on the substrate to be semi-dried; and coatingthe semi-dried polymer layer with a solution including carbon nanotubeshaving guanidine groups dispersed therein.
 9. A method of attachingcarbon nanotubes having guanidine groups to a substrate, comprising:reacting a polymer having crown ether attached thereto with carbonnanotubes having guanidine groups, to prepare a polymer having acombination of crown ether and carbon nanotubes having guanidine groups;and coating a substrate with the polymer having a combination of crownether and carbon nanotubes having guanidine groups.
 10. A method ofattaching carbon nanotubes having guanidine groups to a substrate,comprising: manufacturing a polymer having crown ether attached theretointo a semi-dried film; and coating the semi-dried film with a solutionincluding carbon nanotubes having guanidine groups dispersed therein.11. A method of attaching carbon nanotubes having guanidine groups to asubstrate, comprising: reacting a polymer having crown ether attachedthereto with carbon nanotubes having guanidine groups, to prepare apolymer having a combination of crown ether and carbon nanotubes havingguanidine groups; and manufacturing the polymer having a combination ofcrown ether and carbon nanotubes having guanidine groups into a film.12. The method as set forth in claim 8, wherein the polymer having crownether attached thereto is formed by dispersing 10-20 parts by weight ofcrown ether, based on 100 parts by weight of the polymer, in a solvent,and then stirring the crown ether and the polymer at room temperaturefor 2-5 hrs.
 13. The method as set forth in claim 12, wherein thesolvent is pyridine or pyrrolidine.
 14. The method as set forth in claim12, wherein the crown ether is selected from among 18-member crown etherrepresented by Formula 6, below, dibenzo-18-crown-6-ether represented byFormula 7, below, and dibenzo-24-member crown ether represented byFormula 8, below:


15. The method as set forth in claim 12, wherein the polymer is selectedfrom among polyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), poly(4-vinylphenols),polymethylmethacrylates, and polystyrenes, and derivatives thereof. 16.The method as set forth in claim 9, wherein the polymer having crownether attached thereto is formed by dispersing 10-20 parts by weight ofcrown ether, based on 100 parts by weight of the polymer, in a solvent,and then stirring the crown ether and the polymer at room temperaturefor 2-5 hrs.
 17. The method as set forth in claim 16, wherein thesolvent is pyridine or pyrrolidine.
 18. The method as set forth in claim16, wherein the crown ether is selected from among 18-member crown etherrepresented by Formula 6, below, dibenzo-18-crown-6-ether represented byFormula 7, below, and dibenzo-24-member crown ether represented byFormula 8, below:


19. The method as set forth in claim 16, wherein the polymer is selectedfrom among polyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), poly(4-vinylphenols),polymethylmethacrylates, and polystyrenes, and derivatives thereof. 20.The method as set forth in claim 10, wherein the polymer having crownether attached thereto is formed by dispersing 10-20 parts by weight ofcrown ether, based on 100 parts by weight of the polymer, in a solvent,and then stirring the crown ether and the polymer at room temperaturefor 2-5 hrs.
 21. The method as set forth in claim 20, wherein thesolvent is pyridine or pyrrolidine.
 22. The method as set forth in claim20, wherein the crown ether is selected from among 18-member crown etherrepresented by Formula 6, below, dibenzo-18-crown-6-ether represented byFormula 7, below, and dibenzo-24-member crown ether represented byFormula 8, below:


23. The method as set forth in claim 20, wherein the polymer is selectedfrom among polyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), poly(4-vinylphenols),polymethylmethacrylates, and polystyrenes, and derivatives thereof. 24.The method as set forth in claim 11, wherein the polymer having crownether attached thereto is formed by dispersing 10-20 parts by weight ofcrown ether, based on 100 parts by weight of the polymer, in a solvent,and then stirring the crown ether and the polymer at room temperaturefor 2-5 hrs.
 25. The method as set forth in claim 24, wherein thesolvent is pyridine or pyrrolidine.
 26. The method as set forth in claim24, wherein the crown ether is selected from among 18-member crown etherrepresented by Formula 6, below, dibenzo-18-crown-6-ether represented byFormula 7, below, and dibenzo-24-member crown ether represented byFormula 8, below:


27. The method as set forth in claim 24, wherein the polymer is selectedfrom among polyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), poly(4-vinylphenols),polymethylmethacrylates, and polystyrenes, and derivatives thereof. 28.The method as set forth in claim 10, wherein the polymer is selectedfrom among polyacetylenes, polyphenylenes, polyanilines, polythiphenes,polypyrroles, mixtures of poly(3,4-ethylenedioxythiophenes) andpoly(styrenesulfonic acids) (PEDOT:PSS), and poly(4-vinylphenols), andderivatives thereof.
 29. The method as set forth in claim 11, whereinthe polymer is selected from among polyacetylenes, polyphenylenes,polyanilines, polythiphenes, polypyrroles, mixtures ofpoly(3,4-ethylenedioxythiophenes) and poly(styrenesulfonic acids)(PEDOT:PSS), and poly(4-vinylphenols), and derivatives thereof.
 30. Themethod as set forth in claim 9, wherein the polymer having a combinationof crown ether and carbon nanotubes having guanidine groups is formed byadding the carbon nanotubes having guanidine groups in an amount of1/100-1/500, based on the weight of the polymer having crown etherattached thereto, to a solvent, and reacting the carbon nanotubes havingguanidine groups with the polymer having crown ether attached thereto atroom temperature for 20-40 min.
 31. The method as set forth in claim 11,wherein the polymer having a combination of crown ether and carbonnanotubes having guanidine groups is formed by adding the carbonnanotubes having guanidine groups in an amount of 1/100-1/500, based onthe weight of the polymer having crown ether attached thereto, to asolvent, and reacting the carbon nanotubes having guanidine groups withthe polymer having crown ether attached thereto at room temperature for20-40 min.
 32. The method as set forth in claim 30, wherein the solventis pyridine, pyrrolidine, or methylene chloride.
 33. The method as setforth in claim 31, wherein the solvent is pyridine, pyrrolidine, ormethylene chloride.
 34. The method as set forth in claim 8, wherein thecoating is performed to a thickness of 200-1000 μm.
 35. The method asset forth in claim 9, wherein the coating is performed to a thickness of200-1000 μm.
 36. The method as set forth in claim 10, wherein the filmhas a thickness of 1-2 mm.
 37. The method as set forth in claim 11,wherein the film has a thickness of 1-2 mm.
 38. A method of attachingcarbon nanotubes having guanidine groups to a substrate, comprising:dipping an anodized aluminum oxide substrate, which is installed as acathode, into a solution including carbon nanotubes having guanidinegroups dispersed therein; and performing electrophoresis orelectroplating.
 39. The method as set forth in claim 38, wherein theelectrophoresis or electroplating is performed using direct current of20-50 V for 10-20 min.
 40. A substrate having carbon nanotubes attachedthereto, comprising: a substrate; a polymer layer having crown etherattached thereto; and a coating layer of carbon nanotubes having one ormore bonded moieties, in which the moiety is represented by Formula 1,below:


41. A substrate having carbon nanotubes attached thereto, comprising: asubstrate; and a polymer layer formed by reacting a polymer having crownether attached thereto with carbon nanotubes having one or more bondedmoieties, in which the moiety is represented by Formula 1, below:


42. The substrate as set forth in claim 40, wherein the polymer layer isa coating layer or a film layer.
 43. The substrate as set forth in claim41, wherein the polymer layer is a coating layer or a film layer. 44.The substrate as set forth in claim 40, wherein the crown ether isselected from among 18-member crown ether represented by Formula 6,below, dibenzo-18-crown-6-ether represented by Formula 7, below, anddibenzo-24-member crown ether represented by Formula 8, below:


45. The substrate as set forth in claim 41, wherein the crown ether isselected from among 18-member crown ether represented by Formula 6,below, dibenzo-18-crown-6-ether represented by Formula 7, below, anddibenzo-24-member crown ether represented by Formula 8, below:


46. The substrate as set forth in claim 40, wherein the polymer isselected from among polyacetylenes, polyphenylenes, polyanilines,polythiphenes, polypyrroles, mixtures ofpoly(3,4-ethylenedioxythiophenes) and poly(styrenesulfonic acids)(PEDOT:PSS), poly(4-vinylphenols), polymethylmethacrylates, andpolystyrenes, and derivatives thereof.
 47. The substrate as set forth inclaim 41, wherein the polymer is selected from among polyacetylenes,polyphenylenes, polyanilines, polythiphenes, polypyrroles, mixtures ofpoly(3,4-ethylenedioxythiophenes) and poly(styrenesulfonic acids)(PEDOT:PSS), poly(4-vinylphenols), polymethylmethacrylates, andpolystyrenes, and derivatives thereof.
 48. A substrate having carbonnanotubes attached thereto, comprising: an anodized aluminum oxidesubstrate; and carbon nanotubes having one or more bonded moietiesinserted into pores of the substrate, in which the moiety is representedby Formula 1, below: